1. Field of the Invention
The present invention relates generally to a fixture and method for attaching multiple components together at one time. More particularly, it relates to such a fixture and method which simplifies and improves the assembly of electronic components. Most especially, the invention relates to such a fixture and method which reduces the amount of time that parts of the electronic component assembly are exposed to high temperatures needed for epoxy cure or solder reflow by combining several assembly steps which would normally occur sequentially into one step. The invention further relates to a method which will allow two parts to be bonded together at a low clamping pressure to generate thinner joints. This method is usable separately or in combination with the fixture and method for attaching many components together at one time.
It is often desirable to have very thin adhesive joints between two parts. As an example, the joint between an integrated circuit chip and a heat sink offers the best heat transfer when the joint is very thin.
2. Description of the Prior Art
Electronic parts are assembled conventionally in the following manner: A package is first attached to a substrate, slug or heat sink surface, referred to hereafter for convenience as a heat sink. After that, an integrated circuit chip is attached to the heat sink. Both operations involve high temperatures and significant assembly time.
A similar approach is used to manufacture a multi chip unit (MCU) for the VAX 9000 computer system. For the MCU, several chips are bonded onto a common surface at one time. No other parts are bonded at this time, nor are more mating parts bonded at the same time.
When two flat surfaces are squeezed together with a flowing adhesive between them, the pressure that builds up in the adhesive is highest in the center. Joints of very large area have very large pressure gradients in them because the adhesive must flow a long distance when it is squeezed. Therefore, large area joints are usually thicker than small area joints. To make bonds thin, conventional techniques require high normal pressures to squeeze the joint together.
Escape paths are used in the manufacture of wooden parts, where the glue that forms a joint travels through a small channel. A wooden dowel that is pressed into a hole filled with glue will often have grooves running along its axis to allow glue to escape.
Some epoxy films are made with a support matrix of fiberglass that, by the nature of its shape, forms indentations, but not perforations. Manufacturers usually make an effort to reduce these indentations.
A need therefore exists for improvement in component attachment fixtures and methods, and in methods for producing thin adhesive joints.